Candida albicans is the leading fungal pathogen in normal hosts and in patients with damaged immune systems. In normal hosts, disease caused by C. albicans ranges from mild, easily treated, superficial disease (e.g., thrush in newborn infants; paronychia in workers whose hands are immersed in water) to more severe, chronic or recurrent infections (e.g., candidal vaginitis). It is estimated that 5% of women of child-bearing age will suffer from recurrent candidal vaginitis (Hurley, "Trends in candidal vaginitis." Proc. R. Soc. Med. 70 (Suppl. 4), 1-8 (1970), and that virtually every woman will experience at least one episode during her reproductive years. Vaginitis is particularly frequent in otherwise normal females with diabetes or a history of prolonged antibiotic or oral contraceptive use. While short-term topical therapy is effective in treating individual episodes of vaginitis, such agents do not prevent recurrences. Thus, even in the normal host, infection with C. albicans can occur at epithelial surfaces, and recurrences are not prevented by presently available therapies.
In immunocompromised hosts such as cancer patients, transplant patients, post-operative surgical patients, premature newborns, or HIV-infected people, C. albicans ranks as the leading fungal pathogen. In this population, disease ranges from aggressive local infections such as periodontitis, oral ulceration, or esophagitis in HIV-infected patients, to complex and potentially lethal infections of the bloodstream with subsequent dissemination to brain, eye, heart, liver, spleen, kidneys, or bone. Such grave prognoses require more toxic therapy, with attendant consequences from both the underlying infection and the treatment. Here again, the infection typically begins at an epithelial site, evades local defenses, and invades the bloodstream in the face of immunosuppression. Strategies to interrupt candidal adhesion therefore have broad applicability to the prevention of mild but recurrent disease in the normal host and to the reduction of substantial morbidity and mortality in the immunocompromised.
It is well recognized that C. albicans adheres to epithelial and endothelial cells in the human host, oftentimes by recognizing proteins of the extracellular matrix called ligands. These ligands include proteins such as fibronectin, vitronectin, fibrinogen, the C3 degradation fragment iC3b, or the shorter C3 degradation fragment C3d. Because recognition of all of these proteins except C3d is dependent upon the amino acid sequence ARGININE-GLYCINE-ASPARTIC ACID or R-G-D, these candidal adhesions are thought to operate like the vertebrate integrins and are called "integrin-like proteins" or "integrin analogs."
Vertebrate integrins are composed of two subunits: an .alpha.-subunit and a .beta.-subunit. There are approximately 14 .alpha. and 8 .beta. subunits described to date in vertebrate cells. Using monoclonal or polyclonal antibodies to vertebrate integrins, several investigators have obtained evidence for integrin-like proteins in C. albicans: an .alpha.M analog, an .alpha. 5/.beta.1 complex, or a .beta.1 analog. Neither the .alpha. 5/.beta.1 complex nor the .beta.1 analog has been isolated from C. albicans or from any other candidal species, and the responsible genes encoding these "integrin-like proteins" have not been identified.